Sponbonded nonwoven webs have been produced commercially for many years. As taught in U.S. Pat. No. 3,692,618, they are made by extruding a molten thermoplastic polymer through a spinneret to form an array of closely spaced filaments. The filaments are drawn aerodynamically by means of an air gun (also known as an aspirator jet or a pneumatic jet). Air at a pressure of between about ten and twenty atmospheres is introduced into the air gun to produce a supersonic flow of a column of air that surrounds the filaments and draws them at a rate of between about 3000 and 8000 meters per minute. The drawn filaments are then deposited on a web-forming surface, such as an endless moving belt, where they form a web of entangled continuous filaments lightly bonded at their crossover points. The web may be further bonded, if desired, by passing it through the nip of a pair of heated embossing rolls.
Although prior patents relating to the spunbond process generally teach that any polyolefin may be employed as the thermoplastic polymer, prior to this invention commercially acceptable results were obtained only with polypropylene and high density polyethylene homopolymer as the polyolefin. It would be desirable to form a spunbonded web from a low density polyethylene because of its softer feel, but conventional low density polyethylene does not have adequate melt strenth to form drawn filaments. Linear low density polyethylene (LLDPE) would be expected to provide better results than conventional low density polyethylene, but initial attempts to use LLDPE were not successful because the polymer had inadequate melt strength, i.e., the filaments broke as they were drawn.